The present invention relates to a vane-type motor or pump including a rotor disposed in a housing, a plurality of cam ring members surrounding the rotor in axially disposed side-by-side relationship including sets of vanes respectively associated with a cam ring and displaceable in radially extending slots in the rotor and subdividing a working chamber disposed between the rotor and cam rings. Inlet and outlet orifices lead into working cells and cheek plates laterally confine the working chamber.
A vane-type motor of this type is disclosed in U.S. Pat. No. 3,455,245. This conventional vane-type motor includes two vane-type units disposed in a housing in axial side-by-side relationship which respectively include a cam ring, vanes and rotor element located between two cheek plates. The cam rings have identical stroke curves over which the vanes move and with respect to their stroke curves are in axial alignment. The two cam rings are disposed non-rotatably relative to one another and relative to the two cheek plates. In such a vane-type motor, the volumetric displacement of the motor or pump can be changed only in steps by changing the number of axially aligned units.
The periodical "Oelhydraulik Und Pneumatik" 19 (1975), No. 3, at pp. 153 et seq. describes an infinitely variable double-acting vane-type pump having only one cam ring rotatable relative to the inlet and outlet orifices for changing the volumetric displacement. An arrangement of this type produces adverse flow conditions likely to result in excessive pressure pulsations which require costly efforts for compensating the resultant disadvantageous effects.
U.S. patent application Ser. No. 805,345 now U.S. Pat. No. 4,659,294 discloses a vane-type motor including structures directed to overcoming the shortcoming heretofore experienced. That device includes at least one stroke ring that is rotatable in the circumferential direction relative to another stroke ring. A particularly simple form of this sort of vane-type motor provides for two stroke rings one of which is non-rotational. This device has the advantage that the displacement temporarily occurring due to rotation of one cam ring in a direction opposite to the normal direction of flow is substantially compensated by the stationary cam ring. Pressure pulsations and resultant torque fluctuatios and noises in this pump are relatively well controlled.
Although this type pump is an improvement, undesirable pressure fluctuations and noise problems still occur in the inlet channel and in the return line In particular, pronounced back-pressure pulsations are generated when rotation of the above cam ring creates a closed portion of the working chamber in which pressure fluid is trapped and compressed.